ACE728E datasheet(5/8 Pages) ACE

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ACE728E

42V Input Standoff Voltage, Step-Down LED Driver

VER 1.1

APPLICATION INFORMATION

Setting LED Current

The current sense resistor is inserted between the anode of LED and GND. The current sense resistor

value is calculated as:R1=0.155V／lLED For 1A LED current, choose R1=155

Mω

Inductor Selection

The peak-to-peak ripple is limited to 30% of the maximum output current.This places the peak current far

enough from the minimum overcurrent trip level to ensure reliable operation while providing enough

current ripples for the current mode converter to operate stably. In this case, for 1A maximum output

current, the maximum inductor ripple current is 300 mA.The inductor size is estimated as following

equation: LIDEAL=(VIN(MAX)-VOUT)/IRIPPLE*DMIN*(1/FOSC).

Therefore, for VOUT=5V, The inductor

values is calculated to be L = 15μH. Chose 10μH or 15μH

For VOUT

=3.3V, The inductor values is calculated to be L = 4.9μH. Chose 4.7μH

Output Capacitor Selection

For most applications a nominal 22μF or larger capacitor is suitable. The ACE728E internal

compensation is designed for a fixed corner frequency that is equal to

= 10Khz. For example,

for VOUT

=5V, L=15μH, C

OUT

=22μF.

The output capacitor keeps output ripple small and ensures control-loop stability. The output capacitor

must also have low impedance at the switching frequency. Ceramic, polymer, and tantalum capacitors are

suitable, with ceramic exhibiting the lowest ESR and high-frequency impedance. Output ripple with a

ceramic output capacitor is approximately as follows:VRIPPLE = IL(PEAK)

[1 / (2π x f

OSC x COUT)].

If the capacitor has significant ESR, the output ripple component due to capacitor ESR is as follows:

VRIPPLE(ESR) = IL(PEAK) x ESR

Input Capacitor Selection

The input capacitor in a DC-to-DC LED Driver reduces current peaks drawn from the battery or other

input power source and reduces switching noise in the controller. The impedance of the input capacitor at

the switching frequency should be less than that of the input source so high-frequency switching currents

do not pass through the input source.The output capacitor keeps output ripple small and ensures

control-loop stability

Dimming Control

A typical application of ACE728E with PWM dimming control is shown at right-hand, please contact ACE

engineers’ technical support for defining the peripheral R, C values.

ACE728E Datasheet(PDF) 5 Page - ACE Technology Co., LTD.

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